Why a pine cone closes in water — and opens again

A dry pine cone looks still. Water can change its shape, and drying can change it back. Try a small investigation: make a prediction, observe the same scale, then uncover the explanation.

By Coru · Published 2026-10-25 · Updated 2026-10-25

A mystery in your hand

Picture an open pine cone with wide gaps between its scales. You place it in water. After a while, the gaps narrow. Later, the cone dries and opens again. What moved it, if it had been lying on the ground for ages?

Before trying the activity, write a one-line explanation. Did the cone come back to life? Did water simply press the scales shut? Did the material itself change? Keep your guess until the reveal.

Two cones, one change

You need two similar dry, open pine cones, a bowl of room-temperature water, a plate, paper, a clock and a camera phone. A spoon is useful if the cone floats. Choose intact fallen cones without paint or varnish, and collect only where permitted. With just one cone, you can follow its whole cycle, but you will lose the direct comparison with a dry cone.

Label the places for your cones A and B. Photograph both from the side. On each, choose an easily recognised scale about halfway up; keep comparing that same scale.
Put A in the bowl so that water covers its scales. If it floats, gently turn it with a spoon from time to time. Leave B dry nearby.
Check after 15, 30 and 60 minutes. Record whether the gaps on A have narrowed, widened or stayed the same. Check B at the same time. These intervals are an observation schedule, not a promise that a cone will close within an hour.
Lift A out, let the water drain and leave it on a plate to dry at room temperature. Compare it with the first photograph later and the next day. Record no visible change too. Keep heating out of this activity: you are testing wetting and drying.

A record you can compare

Date and time: __________
A: dry / in water / drying
Chosen scale on A: __________
Same scale in the first photograph: __________
Change in dry cone B: __________
Observation: __________
My explanation: __________

An observation describes a visible change. An explanation proposes a cause; keep them separate.

The reveal: the material does the moving

In a mature cone, this movement can happen through the nonliving tissues of its scales. They take up and lose water. Different regions change their dimensions and mechanical properties differently, making a scale bend. Wetting usually closes this kind of cone; drying opens it. The movement is passive: it needs no living motor or command from the tree.

Imagine a strip made from joined materials that lengthen by different amounts when wetted: the strip will bend. A real scale is more complex. Studies show that several tissues take part; saying that one layer does not respond to water at all is too simple.

Opening in dry conditions helps release seeds that travel on the wind. Your fallen cone may already have shed its seeds; they do not have to be present for its shape to change.

What you found — and what you did not

If A closed after wetting and opened after drying while B barely changed, you observed a reversible change in shape associated with water. This home activity does not reveal the tissues inside: the mechanism comes from research.

One pair of cones does not establish a rule for every species. Cone size, condition and surroundings affect the observation; matching response times are not guaranteed. If nothing visibly happens, keep the record and try another intact open specimen when one is available.

The cone in your bowl has not predicted rain. You changed the water around it. Its shape alone does not give an exact reading of air humidity or replace a weather forecast.

Return to your first guess. What needs changing? The most interesting movement in this activity may be the change in your explanation.